In many applications, such as manufacturing and machining quality control, dimensional information about objects must be accurately measured. Different types of apparatus known as “CMM” (Coordinate Measuring Machine) exist for that purpose using either of a contact type probe or a non-contact type probe mounted on a robotic or CNC machine arm for displacement. However, contact type probes are subject to costly damages in the event of a crash due to their closer behavior with the object, which is less of a problem with non-contact probes such as optical probes. Nevertheless, optical probes of the prior art have a generally lower resolution and none of the existing probes allow for the simultaneous measurement of a plurality of points without moving the supporting arm, which further increases the cumulative error on the measured values.
It is known in the art of non-contact dimensional measurement probes to use a source of substantially collimated generally monochromatic light such as a single point laser beam to measure dimensional properties of objects (targets), such as manufactured or machined parts or assemblies, using a triangulation technique. Basically, dimensional measurements are performed by determining distances between a reference point and a measured point of an object toward which a laser beam is aimed.
According to the well known principle of optical triangulation taught namely in U.S. Pat. No. 6,211,506 entitled “Method and Apparatus for Optically Determining the Dimension, Location and Attitude of Objects”, issued to Pryor at al. in April 2001, the distance between a reference point and a measured point is a function of the angle made by the reflected/scattered light from the beam hitting the object's surface, the angle being obtained from the analysis of the image formed by the scattered light on an appropriately positioned photoelectric detector such as a CCD digital camera (linear or 2D matrix) through appropriate optical devices. However, the single directional light beam suffers from numerous limitations. For example, measuring drilled bore diameters or slopes requires complex supporting arm displacements which introduce mechanical errors and are time consuming or may not be possible at all in the case of small holes.
In an attempt to solve some of these problems of the prior art probes and methods, probes using a beam splitter to provide two parallel laser beams, each beam being detected by its own detector, have been developed. U.S. Pat. No. 6,211,506 entitled “Method and apparatus for electro-optically determining the dimension, location and attitude of objects” issued to Pryor et al. in April 2001 discloses such a probe. Although that technique may be helpful for rapid measurement of certain slopes, it still does not enable measurements in small deep cavities nor provide the flexibility for performing measurements in two or three orthogonal axis at the same time to speed up the procedure, while optimizing accuracy. Providing a plurality of non-parallel diverging beams could help facing such challenges and could also prevent collisions between the probe and the object by enabling “visual” feedback during displacements.
In U.S. Pat. No. 4,766,305 entitled “Optical surface test apparatus for testing constricted surface areas” issued to Fahl in August 1988, a specially designed probe is provided for the acquisition of dimensional data about constricted areas such as bore holes. However, it is still limited to one measure at a time and can not be reconfigured for the acquisition of surface profile data, having its single laser beam oriented perpendicular to the probe axis. Furthermore, it does not enable simultaneous measurements of a plurality of points in potentially different directions.
Therefore, it is desired to overcome or reduce at least some of the above-described problems and limitations of the prior art.